The invention relates to a process as well as an apparatus for the manufacture of flame-retardant oxide of sub-micron size, particularly antimony oxide, using a vaporization zone which is followed by a quenching zone.
U.S. Pat. No. 3,449,072 describes the production of a metallic oxide from the corresponding oxy-halide salt by oxidation of a halide; the reaction between the salt concerned, and oxygen takes place at a temperature which permits the oxide vapor to be cooled rapidly on leaving the vaporization zone.
This process, however, does not allow industrial scale production of finely divided solids in the form of submicron-sized particles, such as are required for filler materials in plastics and textiles.
In particular, antimony oxide, with a particle size of 0.2-5 microns and a specific surface area of 1-5 m.sup.2 /g, has been added for some time now as a flame-retarding agent to various plastics containing chlorides, especially to polyvinyl chloride. In spite of the fact that it is known that the flame-retarding effect is directly dependent on the surface area of antimony oxide particles present, it has not been possible up to now to produce economically, sufficiently fine powders in large quantities.